INTRODUCTION
Rheumatic heart disease (RHD) is a major sequelae of Streptococcus pyogenes characterised by a chronic impairment of the heart valves. Existing research highlights systemic immune dysregulation following infection, which involves sustained elevation of cytokines in patients with the preceding rheumatic fever. However, the mechanisms underlying valve-specific inflammation remains unclear.
AIMS
Our aim was to investigate the effects of circulating cytokines on the valve interstitum using stem cell-derived heart valves to overcome the challenges with studying this human-exclusive pathology.
METHOD
We employed a 3-dimensional organoid model of human heart valves (hVO) using human induced pluripotent stem cells (hiPSCs) previously developed in our lab. We introduced an in vitro cytokine storm to hVOs by adding recombinant cytokines associated with rheumatic fever (TNFa, IL-6, IL-8) to culture. Global proteomics and phospho-proteomics analysis using the Astral Orbitrap were conducted to identify disease-initiating mechanisms. Tissue morphology following cytokine culture was assessed using histology, immunofluorescent labelling and functional read-out of tissue fibrosis.
RESULTS
Molecular characterisation of hVOs following cytokine addition indicated a proinflammatory milieu within the interstitial tissue. Pathways regulating antigen-presentation, cell migration and matrix remodelling were enriched. These changes impacted tissue morphology and passive tension of tissue matrix to indicate tissue fibrosis in response to cytokines alone.
CONCLUSION
Our study suggests that early-phase cytokines may prime the valve interstitium for downstream immune infiltration by promoting migration and activation of immune effector cells. Our ongoing work is incorporating the valve endothelium into our model, to explore their role in cytokine-mediated pathogenesis.